Marine navigation binoculars with virtual display superimposing real world image

ABSTRACT

A system including binoculars augmented with a computer-generated virtual display of navigation information (hereinafter referred to as “nav glasses”) and marine navigation systems employing such binoculars. The computer-generated display is superimposed on the real world image available to the user. Nav glasses also have the components needed to link them to a navigation system computer which is utilized to generate the see-through display of the navigation information. They are preferably equipped with sensors compass and an inclinometer for acquiring azimuth and inclination information needed by the navigation computer and a sensor for measuring any magnification of the field of view. The nav glasses can be employed to lock onto a moving target, which can then be tracked by onboard radar. The navigation system in which the nav glasses are incorporated also accept inputs from other sources such as a shipboard compass, a GPS, and other navigation aids; and a route planning system. The field of view of the nav glasses is calculated from information obtained from the nav glasses and navigation sensors, and a display manager generates a pre-fetch display of navigation information from the route planning and radar inputs. This pre-fetch display or image extends well beyond the nav glass field of view. Consequently, as the glasses are shifted from side-to-side or up or down, all that may be required to match the virtual display to the real world image is to align a different segment of the pre-fetch image with the actual field of view. Once the alignment of the virtual display of navigation information and the actual field of view is completed, the virtual overlay is transmitted in coded form to a video output component of the navigation computer and forwarded to the nav glasses where the virtual display is constructed and superimposed on the real world view.

RELATED APPLICATION

This application is based on prior copending provisional applicationSer. No. 60/015,954, filed Apr. 24, 1996, the benefit of the filing dateof which is hereby claimed under 35 U.S.C. §§ 119(e) and 120.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to novel, improved navigation aids and,more specifically, to marine binoculars augmented with a visual displayof navigation information and to marine navigation systems employingsuch binoculars.

BACKGROUND OF THE INVENTION

Ships and boats at sea need a variety of information in order tonavigate safely. This information includes: the vessel's positionrelative to its planned course; the vessel's position relative tovisible navigation hazards such as land masses and other ships; and thevessel's position relative to hidden hazards such as submerged rocks,channel boundaries, shipping lane separation zones, and restrictedareas. The mariner acquires this information in a number of ways.

The first is by visual reference. By monitoring the vessel's positionrelative to known points of land, often with the aid of a compass, thenavigator can triangulate the ship's position relative to its intendedcourse. By monitoring other vessels, the navigator calculates whether acourse change will be required to avoid a collision. And, by monitoringthe ship's position relative to buoys, lights, and other visual aids tonavigation, the mariner can also avoid some of the unseen hazards tonavigation.

This same information is commonly augmented by radar which also displaysthe ship's position relative to visible hazards such as land masses andother vessels. In addition, the radar, with input from the ship's gyroor magnetic compass, can more accurately calculate range and bearing andperform collision avoidance calculations.

To best avoid unseen navigation hazards such as submerged rocks, thenavigator needs to continuously calculate the absolute geographicposition of the vessel and plot that position against a nautical charton which the hidden hazards to navigation are indicated. This process isgreatly facilitated by use of a Global Positioning Systems (GPS)receiver and an Electronic Chart System (ECS). The ECS displays adigital representation of a conventional paper nautical chart. On thischart, the ECS overlays the position of the ship based on input from theGPS. The ECS usually consists of a navigation computer containing anelectronic nautical chart (ENC) database, interfaces to navigationsensors such as those identified below, and a fairly high resolutioncomputer display screen.

While the ECS represents a vast improvement over manually plotting theship's position against a paper chart, it has a number of drawbacks andlimitations. The first is that it is often difficult to relate: (a) theinformation in the electronic chart display (usually oriented course-up)with (b) the real world as seen from the navigator's field of view(often a completely different direction). A second significantlimitation is that the ECS requires a color, fairly high resolution(therefore fairly large size) display to be most effective. Manymariners, however, navigate from an open cockpit or a flying bridgeconning station. There, the lack of space, glare from direct sunlight,and exposure to the elements limit the utility of an ECS display.

Others have attempted to improve marine navigation by augmenting marinebinoculars with information pertinent to navigation. Heretofore, theseattempts have been limited to adding only bearing and, in a few cases,distance information. This information is at best of limited utility inidentifying hidden obstacles and other unseen hazards to navigation.Furthermore, these products usually split the field of view between thereal world image and an image of a compass, using mirrors and normallens optics. This is awkward and can actually distract from instead ofenhance the real world image available to the mariner.

From the foregoing, it will be apparent to the reader that there is apresent and continuing need for better aids to marine navigation.

SUMMARY OF THE INVENTION

The need for improved navigation aids has now to a significant extentbeen satisfied by instruments which embody the principles of the presentinvention and are referred to hereinafter as “nav glasses.”

Nav glasses are, generally speaking, marine binoculars augmented with asee-through, computer-generated overlay or display of navigationinformation. The computer-generated display is superimposed on the realworld image available to the user.

Nav glasses also have the components needed to link them to thenavigation computer which is utilized to generate the see-throughdisplay of navigation information. Also, they typically are equippedwith instruments such as a fluxgate compass and an inclinometer foracquiring azimuth and inclination information needed by the navigationcomputer. In appropriately configured navigation systems, the navglasses can be employed to lock onto a moving target, which can then betracked by onboard radar.

The navigation systems in which the nav glasses are incorporated alsoaccept inputs from other sources such as a compass, a GPS, and othernavigation aids; a route planning system; and onboard radar. The fieldof view of the nav glasses is calculated from information obtained fromthe nav glasses and navigation sensors, and a display manager generatesa pre-fetch display of navigation information from the route planningand radar inputs. This pre-fetch display or image extends well beyondthe nav glass field of view. Consequently, as the glasses are shiftedfrom side-to-side or up or down, all that is required to match thevirtual display to the real world image is to align a different segmentof the pre-fetch image with the actual field of view. This is animportant feature of the present invention inasmuch as thejust-described approach is much faster then generating a new virtualimage each time the nav glasses are shifted. If the field of view liesbeyond the boundaries of the current pre-fetch image or overlay, a flagis raised; and a new pre-fetch overlay is generated and aligned with thecurrent field of view.

Once the alignment of the virtual display of navigation information andactual field of view is completed, the virtual overlay is transmitted indigital form to a video output component of the navigation computer andforwarded to the nav glasses where the virtual display is constructedand superimposed on the real world field of view. Also important is anavigation system feature which allows additional, textual informationto be added to the virtual display at the option of the user of the navglasses. The user also has the option of canceling the display of theadditional information at any time.

The advantages, features, and objects of the present invention will beapparent to the reader from the foregoing and the appended claims and asthe detailed description and discussion of the invention proceeds inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a marine navigation system whichincludes nav glasses embodying the principles of the present invention;

FIG. 2 is a top view of the nav glasses depicted in FIG. 1;

FIG. 3 is a bottom view of the nav glasses;

FIG. 4 is an end view of the nav glasses;

FIG. 5 is a block diagram showing the components of the FIG. 1 navglasses;

FIG. 6 is a fragment of a conventional marine navigation chart;

FIGS. 7 and 8 are companion representations of the real world image andvirtual overlay available to the user of nav glasses embodying theprinciples of the present invention;

FIG. 9 is a fragment of a second marine navigation chart;

FIGS. 10 and 11 are companion representations of a real world view andvirtual display of navigation information available to the user of thenav glasses; in this instance, the virtual display involves athree-dimensional projection of navigation data; and

FIGS. 12A AND 12B, taken together, constitute a flow diagram depictingthe operation of the FIG. 1 navigation system.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing, FIG. 1 depicts an onboard navigationsystem 20 which includes a computer 22, a transceiver 24, and navglasses 26 which embody, and are constructed in accord with, theprinciples of the present invention. Nav glasses 26 provide the marineror other user looking in the direction of arrow 28 with a real world,magnified image of the scene encompassed by the nav glasses field ofview. Superimposed on this image is a virtual, see-through display oroverlay of navigation information. This information may include, but isnot necessarily limited to:

1) azimuth (true)

2) text labels of strategic geographical features on the horizon

3) highlighted symbols indicating positions of navigation aids such asbuoys and lights

4) the intended course line and planned cross-track deviation limits

5) safety depth contour lines

6) a “point-and-click” bullseye target finder

7) highlighted symbols indicating positions of ARPA (Automatic RadarPlotting Aid) targets

8) course, speed, closest point of approach and time to closest point ofapproach for tracked ARPA targets

9) an instrument gauge displaying critical own-ship navigationinformation such as: heading, speed, bearing to waypoint, cross-trackdeviation, depth, and rudder angle

Nav glasses 26 have conventional binocular optics, and the real worldimage is formed by those optics in a conventional manner. The virtualdisplay of navigation information is generated by navigation computer 22and is transmitted to the nav glasses by either the wireless transceivershown in FIG. 1 or by a conventional data cable 30 (see FIGS. 3 and 5)supplied in lieu of or in addition to transceiver 24.

Referring now to FIGS. 3-5, nav glasses 26 include a casing 32 whichhouses the optics that form a real world image of the scene viewed bythe user. The optics of nav glasses 26 are collectively identified inFIG. 5 by reference character 33. They include left and right objectivelens 34L and 34R (see FIGS. 2 and 3) and corresponding eyepieces 36L and36R (see FIG. 4). Rings 38 and 40 allow the user of nav glasses 26 tobring the image formed by optics 33 into sharp focus and to change themagnification offered by nav glasses 26.

Also housed in the casing 32 of nav glasses 26, as best shown in FIG. 5,are: (a) a microprocessor 42 which controls the flow of data to and fromnavigation computer 22; (b) a virtual display head 44 which employsmicro LCD's and a beam splitter virtual retinal display techniques, oran appropriate alternative to superimpose the see-through display ofnavigation information on the real world image generated by binocularoptics 33; (c) a fluxgate compass and inclinometer 46/48 or equivalenttracking mechanism; (d) a wireless modem 50; (e) a connector 52 for datacable 30; and (f) a set of controls collectively identified by referencecharacter 54. The controls include push buttons 56 and 58 withprogrammable functions and a thumb-operated track ball 60. The trackball is employed to position a movable cursor 61 (FIG. 7) on a targetselected by the user of nav glass 26. Push button 58 is then clicked,locking the cursor on the designated target. That enables onboard radarto track the target, making available on the virtual display informationsuch as: the course of the target and its speed, the target's closestpoint of approach, and the time to the closest point of approach.

Nav glasses 26 have two data channels served by the wireless orcable-type data link. These are: (1) a control channel which sendsazimuth and inclination information and the current magnification of thereal world image to navigation computer 22; and (2) a display channelwhich receives the computer generated see-through overlay from thenavigation computer, typically as a standard VGA-type video signal.

Referring now to FIG. 1, navigation computer 22 includes the followingelements:

1) a PC architecture (CPU and system RAM)

2) serial interface ports for receiving navigation information from theGPS and other navigation sensors

3) a control data interface port for receiving azimuth, inclination,magnification, cursor position, and push button status information fromthe nav glasses

4) a video display controller capable of generating and sending astandard VGA video signal to the nav glasses

5) a hard disk or other long-term storage device for ENC storage andretrieval

6) a removable media drive (e.g., floppy, S-RAM, or CD) used for loadingand updating the ENC database

7) software to: (a) process the navigation sensor inputs, (b) processthe azimuth and other control signals from the nav glasses, (c)calculate the angle subtended by the current field of view, (d) use theresulting spatial information to retrieve from the ENC navigationinformation which should be included in the field of view, and (e)generate the see-through display overlay

8) optionally, an available radar interface board which enables theabove-discussed target tracking mode of nav glasses 26.

Other sensors may advantageously be interfaced with digital computer 22to provide to the computer such useful information as rudder angle,engine RPM, propeller pitch, thruster status, and wind force and speed.By interfacing navigation computer 22 both to the GPS and other sensorssuch as those just described, the see-through display available to theuser of nav glasses 26 may also be generated to include a dashboard typeof representation with digital emulations of analog gauges, for examplean emulation of a tachometer.

The details of the several elements of navigation computer 22 are notrelevant to an understanding of the present invention, and they willaccordingly not be discussed herein. Thus, the serial interface ports ofthe navigation computer are shown only schematically and collectivelyidentified by reference 62. These ports input to the computer RAM and/orCPU information supplied by, for example: the Global Positioning System,an onboard compass or gyro compass, a speed log, an echo sounder, ARPAradar, an autopilot, etc. The ENC data storage device is identified byreference character 64 and the drive for the removable data storagedevice is identified by reference character 66. I/O interface portsbetween navigation computer 22 and transceiver 24 (or a data cable suchas that bearing reference character 30) are identified by referencecharacters 68 and 70.

Referring still to the drawing, FIG. 6 is a fragment 72 of a marinenavigation chart covering the Valdez Narrows. FIG. 7 is a pictorialrepresentation 74 of: (a) the real world image 76, and (b) asuperimposed, see-through, virtual display 78 seen by a user of navglasses 26 located at the position identified by reference character 80in FIG. 6 with the nav glasses trained in the direction indicated byreference character 82. As would be expected, geographical features arereadily visible in the real world image as are the manmade structurescollectively identified by reference character 83.

In this representative example, information on: (a) the position 80 ofthe mariner's vessel 84 from the GPS, and (b) azimuth and magnificationinformation from nav glasses 26 is inputted to navigation computer 22;and the ENC database is accessed. Also, if the azimuth is derived from ashaft sensor and is therefore relative, the heading of the vessel,obtained from a magnetic or gyro compass, is inputted to the navigationcomputer.

Navigation computer 22 then calculates the direction and angle subtendedby the field of view of nav glasses 26 ;extracts from the ENC databasepertinent navigation information included within the estimated field ofview using available and proven algorithms; and generates a VGA,see-through image displaying the selected ENC text or labels making upsee-through display 78.

The VGA image is transmitted from navigation computer 22 via transceiver24 to the antenna 86 of modem 50, thence to VGA overlay display head 44,which causes see-through virtual display 78 to be superimposed on thereal world image 76 generated by binocular optics 33 and seen by themariner.

A perhaps more sophisticated application of navigation system 20 ispresented in FIGS. 8 and 9. FIG. 8 is a fragmentary navigation chart 88.FIG. 9 pictorially depicts the real world image 90 and virtual image 92seen by a mariner at position 96 (FIG. 8) with his nav glasses 26trained in the direction indicated by arrow 98. Natural and manmadegeographical features are clearly visible. Also appearing in themariner's field of view in the form of a see-through display are: thecontour line 100 for a water depth of ten meters needed for vessel 94 toproceed in safety, the course 102 to be followed by the vessel to theberth 104 at the end of pier 106, and the allowable limits ofcross-track deviation from the course identified by reference characters108 and 110. In this representative example, therefore, there is adisplay of navigation data with vectors in all three dimensions to aidin the navigation of vessel 94.

Generation of a see-through virtual display with three-dimensional dataas just discussed requires accurate information on azimuth, inclination,and magnification. The requirement for accurate inclination informationcan be relaxed by providing a tick mark (identified by referencecharacter 112 in FIG. 9) at a vertical edge 114 of see-through virtualdisplay 92. The mariner aligns real world image 90 and virtual display92 by registering tick mark 112 with horizon 116. This eliminates theinclination information needed for computer 22 to align the real worldand virtual images.

Referring still to the drawings, the operation of navigation system 20can perhaps best be appreciated by referring to the logic diagram ofFIGS. 12A and 12B in which the depicted boxes represent components,states, or functions, the arrows with solid tails represent the flow ofcontrol, and the arrows with outline tails represent the flow of data.

Available from navigation glasses 26, as discussed above and shown bybox 118 in FIG. 12A, are parameters which describe the orientation ofnav glasses 26. These are the inclination of the glasses provided byinclinometer 48, the heading of the glasses from fluxgate compass 46,and the magnification factor determined by the setting of ring 40. Thisdata is transmitted to navigation computer 22 along with ship headingand position data obtained from navigation sensors such as a gyrocompass and a global positioning system (GPS) receiver (box 120), routeplanning information including way points and the intended track ofvessel 80 or 96 (box 122); the range, bearing, speed, course, closestpoint of approach, and/or time of closest point of approach of targetsbeing tracked by radar (box 124), and inputs from the target-selectingcursor 61 which is employed when more information is wanted on a vessel,obstacle, etc. to which the cursor is locked. Referring now to both FIG.12A and FIG. 12B, the nav glass sensor inputs are continuously monitored(routine 125 a); and the inclination, azimuth, and magnification arecomputed. The navigation sensors are also continuously monitored(routine 125 b), and the ship heading and position are computed from thedata supplied by those sensors. From the parameters justdiscussed—inclination, azimuth, magnification, ship heading, and shipposition—the field of view of the nav glasses is continuously calculated(routine 126 a).

Concurrently, the virtual overlay or image of navigational informationavailable to the user of nav glasses 26 is generated. Specifically,stored chart information is read from the database 127 in storage device66 and transmitted to a display manager 127 a. Typically, thisinformation will provide the locations of charted objects such as buoysand lighthouses, the contours of coastlines, and depth contours. Thevirtual overlay generating process also takes information from a routeplanning system (box 127 b) and provides the relevant information to thedisplay manager 127 a in computer 22. The information includes theintended track of the vessel, the actual track—which may or may notduplicate the intended track—, and a series of way point positions. Theactual route of the vessel is monitored by routine 127 c.

At the same time, the data relevant to radar tracked targets ismonitored (routine 127 d) and transmitted to the display manager. Asshown in FIG. 12A, this data may include: the position, heading, andspeed of the target as well as the closest point of approach to thetarget and the time to the closest point of approach.

The information supplied to the display manager extends over apre-fetched range which encompasses the unmagnified field of view of navglasses 26 but extends well beyond that field in all fourdirections—left, right, up, and down. This formation of the pre-fetchfield is an important feature of the present invention because itminimizes the time required to provide a new virtual display when theuser of the nav glasses 26 slews the glasses to a new direction. Withthe pre-fetch image having already been constructed, all that isrequired to provide the corresponding virtual image when a new field ofview appears in nav glasses 26 is to select the appropriate segment fromthe existing pre-fetch image. This is a much faster process thanbuilding a new image from the information discussed above for the newfield of view.

Another function of computer 22, shown in FIG. 12A, is to monitor thecontrols of nav glass 26; viz. , the position of cursor 61 and thestatus of programmable push buttons 56 and 58 (routine 127 e).

Referring now most particularly to FIG. 12B, reference character 128identifies a routine in which computer 22 determines whether thepre-fetch image encompasses the current field of view of nav glasses 26.If this question is answered in the affirmative, a further determinationis made as to whether a new segment of the pre-fetch image is needed toalign the virtual display with the current field of view of nav glasses26. If computer 22 finds that the virtual image and field of view arealigned, the comparison process continues. If alignment is required tomatch the virtual image to the field of view of nav glasses 26, thepre-fetch image is panned to align the appropriate segment of that imagewith the actual field of view of the nav glasses as indicated in theblock identified by reference character 132. It was pointed out abovethat this is a much simpler and correspondingly faster process ofmatching the virtual display to the actual field of view than is thebuilding a new virtual image from the input data discussed above.

In conjunction with the foregoing, the field of view of nav glasses 26changes when the user of nav glasses 26 adjusts the magnification of navglasses 26 with magnification ring 40. Computer 22 treats a new field ofview attributable to a change in magnification in the same manner as anyother new field of view—i. e. , one resulting from stewing or changingthe inclination of nav glasses 26.

When the comparison routine shown in block 128 determines that a currentfield of view lies beyond the boundaries of the available pre-fetchimage, the boundaries for a new pre-fetch image are calculated (seeblock 134); and a flag is raised, indicating that a pre-fetch image withnew boundaries is needed. The new pre-fetch overlay is created with theroutine identified by reference 136. Specifically the new boundaries aretransmitted to display manager 126 b. The display manager responds bysupplying to routine 136 the current data from the sources identified inblocks 118, 120, 122, and 124 and the information from database 127needed to create the new pre-fetch overlay.

The new pre-fetch image is supplied to the comparison routine (block128). Because the new pre-fetch image extends beyond the current fieldof view to the left and right of and above and below the current fieldof view, routine 128 finds that the current field of view is within theboundaries of the new pre-fetch overlay and passes that information toroutine 132 to align the new pre-fetch image with a current field ofview.

Once the actual field of view is aligned with the virtual image, thevirtual image in coded form is routed to video output 138 of computer22. The signal from the video output is transferred as by data cable 30to nav glasses 26. There, the virtual image is formed as an overlay tothe real world image by virtual display head 44 under the control ofmicroprocessor 42.

Referring still to FIG. 12B, there are circumstances in which additionalinformation on a virtually displayed object can be beneficial. Forexample, in a typical scenario involving a navigation light, it may beadvantageous to know that the light is red, flashes on a two secondcycle, lies eight miles from the vessel equipped with system 22, andlocates the entrance to a strait. This information can be provided to awindow in the virtual display seen by the user of the nav glasses 26 byinvoking the routine identified by reference character 140 as caninformation on vessels being tracked by radar and other usefulnavigational information.

In applications of the invention involving the supply of additionalobject information, one of the nav glasses pushbuttons (for example,pushbutton 58) is programmed as discussed above to function as a querybutton and the second pushbutton 26 is employed to lock cursor 61 onto aselected object or target.

A routine 141 (see FIG. 12A) continuously monitors the position ofcursor 61, the status of cursor lock button 56, and the status of querybutton 58 and reports to interface manager 142 on the status of thepushbuttons and the position of the cursor. If the interface managerfinds that the query button has been activated, it raises a flagindicating that this has been done and provides the position of thecursor. Routine 140 then interrogates display manager 127 a, retrievingthe additional information on the object to which the cursor is lockedby the activation of pushbutton 56. With information on that objectavailable from display manager 127 a, routine 140 builds an informationpanel and supplies the data constituting that panel to video output 138.From there the data is routed as by data cable 30 to nav glasses 26.Microprocessor 42 and virtual display head 44 construct the virtualpanel identified by reference character 144 in FIG. 8 from thetransmitted data and add this panel to the virtual overlay shown in thatfigure.

The subsequent opening of query switch 58 invokes the routine identifiedin FIG. 12B by reference character 146. This routine cancels thetransmission of the data from which panel 144 is constructed, and videooutput 138 routes to nav glasses 26 a signal which causes panel 144 todisappear from the virtual display seen by the user of nav glasses 26.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description; and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed:
 1. A navigation system for a marine vessel that employs a composite image produced by superimposing a virtual image comprising navigational data over a real image of a portion of a surrounding environment, comprising: (a) an ocular device comprising a housing in which are disposed a set of positionable optical lenses that image light reflected from the portion of the surrounding environment so as to directly form a field of view of the real image of the portion of the surrounding environment on a user's retina; (b) a virtual image generator that produces an optical signal directed toward the user's retina so as to form a virtual image on the retina, said optical signal being generated in response to a video input signal; (c) an azimuth sensor that produces an azimuth signal, the azimuth sensor being coupled to the ocular device, said azimuth signal being indicative of an orientation of the field of view formed by the ocular device; (d) a plurality of instruments disposed onboard and related to a bearing and position of the marine vessel, including a vessel direction sensor that produces a vessel direction signal indicative of a direction in which the vessel is heading and an absolute position sensing instrument that produces an absolute position signal indicative of a position of the marine vessel; and (e) a navigational computer coupled in communication with the ocular device and the plurality of instruments, said navigational comprising: (i) a processor and a memory for storing machine instructions executable on the processor; (ii) a video display controller that generates the video input signal; (iii) a persistent storage means for storing the navigational data; and (iv) the machine instructions that are stored in the memory, when executed by the processor, cause it to perform a plurality of functions, including: (1) processing the azimuth signal and the absolute position signal, and as a function thereof, determining the field of view produced by the ocular device; (2) determining a portion of the navigational data that should be included in the virtual image, based at least in part upon the field of view that has been determined and the vessel direction signal; and (3) including only said portion of the navigational data thus determined in the composite image.
 2. The navigation system of claim 1, wherein the ocular device has a variable magnification factor control that is user adjustable, further comprising a magnification factor sensor coupled to the ocular device to determine the magnification factor that the user has selected for the ocular device, producing a magnification factor signal indicative thereof, wherein the field of view is also determined as a function of the magnification factor signal.
 3. The navigation system of claim 1, wherein the virtual image includes a tick mark that defines an inclination of the ocular device.
 4. The navigation system of claim 1, wherein the navigational computer is mounted onboard the marine vessel, further comprising a communications link that couples the navigation computer in communication with the ocular device.
 5. The navigation system of claim 1, further comprising an inclination sensor coupled to the ocular device, said inclination sensor sensing an inclination of the ocular device and producing an inclination signal that is used by the processor of the navigational computer to further determine the orientation of the field of view.
 6. The navigation system of claim 1, wherein the navigational data include locations of navigational hazards, and wherein the virtual image graphically displays navigational hazards disposed within the field of view of the ocular device.
 7. The navigation system of claim 1, wherein the processor of the navigational computer processes the vessel direction signal and absolute position signal and displays indicia of a heading direction and a position of the marine vessel in the virtual display.
 8. The navigation system of claim 1, wherein the ocular device comprises binocular optics.
 9. The navigation system of claim 1, wherein the virtual image generator comprises a virtual display head that includes a liquid crystal display and a beam splitter disposed proximate to said liquid crystal display to produce the virtual image.
 10. The navigation system of claim 1, wherein the navigational data include electronic navigational charts stored in the memory, the virtual image comprising at least a portion of a navigational chart corresponding to the field of view of the ocular device.
 11. The navigation system of claim 10, wherein the electronic navigational charts include virtual three-dimensional navigational data, a portion of said virtual three-dimensional navigational data being displayed in the virtual image.
 12. The navigation system of claim 10, wherein the processor of the navigational computer selectively fetches and displays electronic navigational chart data corresponding to a current field of view for generating the virtual image, and prefetches additional electronic navigational chart data corresponding to portions of the real image that are adjacent to but outside a current field of view, the additional electronic navigational chart data being thereby immediately accessible and displayable in the virtual image as the field of view changes to include a portion of the real image that was previously adjacent to, but outside the field of view before it changed.
 13. The navigation system of claim 12, wherein if the field of view changes sufficiently so that a new field of view extends beyond the portions of the real image to which the additional electronic navigational chart data correspond, the navigational computer again fetches navigational chart data corresponding to the new field of view and prefetches new additional electronic navigational chart data corresponding to portions of the real image that are now adjacent to but outside the new current field of view.
 14. The navigation system of claim 10, wherein the electronic navigational charts comprise water depth data, and the virtual image comprises contour lines, each contour line corresponding to a defined depth of water.
 15. The navigation system of claim 10, wherein the electronic navigational charts include textual information pertaining to various charted objects, including navigation buoys, navigation lights, danger points, and coastal contours, portions of the textual information corresponding to such charted objects that lie within the real image field of view being selectively displayed in the virtual image adjacent to said charted objects.
 16. The navigation system of claim 15, wherein the ocular device includes a cursor control that enables the user to position a cursor in the virtual display, the user positioning the cursor over a charted object in the real image and activating a selection control to selectively enable and disable display of the textual information.
 17. The navigation system of claim 15, wherein the textual information is disposed within an information panel displayed in the virtual image.
 18. The navigation system of claim 1, further comprising an onboard radar system that produces a produces a radar image of objects in the surrounding environment, wherein the navigation computer is coupled with the onboard radar system, the ocular device including a control that enables the user to select a target object in the field of view of the real image to be tracked by the onboard radar system, the target object that is selectable by the user including both fixed and moving objects.
 19. The navigation system of claim 18, wherein the ocular device includes a cursor control that enables the user to position a cursor in the virtual display, the user selecting the target object by positioning the cursor over a desired real image object and activating the control to select the target object over which the cursor has been positioned.
 20. The navigation system of claim 18, wherein the target object is a moving object having a position, heading, and speed determined by the onboard radar system and wherein the virtual image includes an indication of at least one of said position, heading, and speed of the target object.
 21. The navigation system of claim 20, wherein the navigational computer determines at least one of an estimated closest point of approach and estimated time of closest point of approach relative to the target object, based on the position, heading, and speed of the target object, and the position, heading, and speed of the marine vessel, the virtual image an indication of said at least one of the estimated closest point of approach and the estimated time of closest point of approach.
 22. The navigation system of claim 1, further comprising a route planning system onboard the marine vessel and coupled in communication with the navigational computer, said route planning system providing route information to the navigational computer.
 23. The navigation system of claim 22, wherein the route planning system provides an intended track to the navigational computer, the virtual image including a representation of at least a portion of the intended track of the vessel.
 24. The navigation system of claim 22, wherein the route planning system provides a set of waypoints to the navigational computer, at least a portion of said waypoints being represented in the virtual image.
 25. The navigation system of claim 22, wherein the route information provided by the route planning system includes a desired course with limits of cross-track deviation from the desired course, the virtual image including indications of the cross-track deviation limits and the desired course.
 26. The navigation system of claim 22, wherein the route information provided by the route planning systems includes an intended track and actual track of the vessel, said intended track and actual vessel track being included in the virtual image.
 27. The navigation system of claim 1, wherein the plurality of onboard instruments include at least one of a rudder angle sensor, engine rotational speed sensor, propeller pitch sensor, thruster status indicator, wind force sensor, and wind speed sensor, the virtual image including an indication of said at least one of the rudder angle, engine rotational speed, propeller pitch, thruster status, wind force, and wind speed.
 28. The navigation system of claim 27, wherein the indication of at least one of the rudder angle, engine rotational speed, propeller pitch, thruster status, wind force, and wind speed is displayed in a virtual dashboard comprising a digital emulation a plurality of analog gauges. 